A vertical Hall sensor is a magnetic field sensor which is sensitive to a magnetic field which extends parallel to the surface of the semiconductor chip. The vertical Hall sensor typically comprises an n-doped well, which has been diffused into a p-doped substrate, or a p-doped well, which has been diffused into an n-doped substrate, the well typically having four or five contacts, which are arranged along a straight line and are located on the surface of the semiconductor chip. Two or three of the four contacts are current contacts which are used for the purpose of causing a current to flow through the vertical Hall sensor, and two of the other contacts are voltage contacts, which are used for the purpose of tapping the Hall voltage, which arises in the presence of a magnetic field that extends perpendicular to the direction of the current.
The most frequently used vertical Hall sensors have four contacts or five contacts or at most six contacts and are sufficiently known from the literature, e.g., from the thesis number 3134 of the Ecole Polytechnique Fédérale de Lausanne by Enrico Schurig, and also from the patent literature, e.g., from U.S. Pat. No. 5,572,058, U.S. Pat. No. 7,872,322, U.S. Pat. No. 7,253,490, U.S. Pat. No. 7,511,484, WO 2010101823. A vertical Hall sensor having more than six contacts is known from US 2010/0133632.
One of the most difficult tasks in the development of the vertical Hall sensors has always been to achieve a high magnetic-field sensitivity, on the one hand, and to keep the so-called offset of the sensor signal, which is the voltage appearing between the voltage contacts in the absence of a magnetic field, as small as possible, on the other hand.
Because of the depth of the well, which is limited by technology to a few micrometers, the contacts must be as close as possible to one another to achieve a high sensitivity. Since typical wells generated by ion implantation and subsequent relatively long diffusion have the highest doping on the surface, however, the main component of the current also flows through the Hall element just below the surface, of course, and is therefore not very effective for generating the Hall voltage, so that the sensitivity is low. In addition, the current pathway between input current contact and output current contact is therefore very short, which has the result that even very small processing tolerances result in a high offset.
A vertical Hall sensor is known from EP 1977460, in which electrically nonconductive regions are arranged between the contacts, which act as barriers, which force the current flowing between the contacts to flow around these barriers into the depth. However, if these barriers are designed as regions having inverted doping, regions free of charge carriers form around them, whose thickness is a function of the respective locally appearing potential difference between the barrier and the surrounding conductive region. Changes of this potential difference cause a change of the geometry of the conductive region. This in turn results in variations of the offset. The offset of the sensor then typically increases with increasing operating voltage and also with increasing ambient temperature.